Processes for forming an aldehyde by the hydroformylation reaction of an olefinic compound with carbon monoxide and hydrogen in the presence of a rhodium complex hydroformylation catalyst and free triarylphosphine are well known in the art and of particular importance are those hydroformylation reactions designed to produce aldehyde products rich in their normal isomers at significantly low pressures, such as taught for example in U.S. Pat. Nos. 3,527,809 and 4,148,830 and commonly assigned copending U.S. patent application Ser. No. 776,934, filed Mar. 11, 1977, now U.S. Pat. No. 4,260,828 (Belgium Pat. No. 853,377).
It is also known that the rhodium complex catalyst loses activity (i.e. becomes partially deactivated) during prolonged use and thus reactivation of such partially deactivated catalysts is of extreme importance to the state of the art due to the high cost of rhodium values. While it is difficult to ascertain all of the reasons for such an activity loss it is believed that in large scale hydroformylation reactions that the loss in activity is due at least in part to the presence of alkyl substituted phosphine in the hydroformylation medium. For instance it is known that the presence of alkyldiarylphosphine in the rhodium complex catalyzed hydroformylation of the alpha-olefin, propylene, inhibits catalyst productivity, i.e. the rate at which the desired product aldehydes are formed. It is further known that when triarylphosphine ligand is employed in the hydroformylation of an alpha-olefin, alkyldiarylphosphine is produced in situ, the "alkyl" group thereof normally being derived from the alpha-olefin undergoing hydroformylation and the "aryl" groups thereof being the same as the aryl of the triarylphosphine and that in a continuous hydroformylation reaction of alpha-olefins in the presence of triarylphosphine ligand to produce aldehydes, the continued build-up of such alkyl substituted phosphines can eventually lead to an unacceptable decrease in the rate of reaction and activity of the rhodium complex catalyst due to the affinity of such alkyl substituted phosphines for the catalyst.
Commonly assigned U.S. patent application Ser. No. 762,335 filed Jan. 25, 1977 (Belgium Pat. No. 863,267) now abandoned in favor of continuation application Ser. No. 140,830 filed Apr. 16, 1980, now U.S. Pat. No. 4,260,828 suggests utilizing the stability effect that alkyldiarylphosphine has on the rhodium catalyst of such hydroformylation reactions by adjusting the reaction conditions to be more severe in order to regain the loss in catalyst productivity, while retaining catalytic activity due to the enhanced catalyst stability attributed to the presence of such alkyldiarylphosphine. However such a procedure is not a totally adequate solution to maintaining the productivity of the catalyst solution.
Commonly assigned U.S. patent application Ser. Nos. 040,913 and 108,279 filed May 21, 1979, now abandoned and Dec. 28, 1979, now U.S. Pat. No. 4,283,304 respectively both disclose a method for removing undesirable alkyl substituted phosphine from a liquid composition containing a rhodium hydroformylation catalyst by treating said composition in the presence of water with an alpha,beta-unsaturated compound or anhydride thereof, e.g. maleic acid or its anhydride, so as to form solubilized reaction products with the phosphines present in said composition and removing said products by phase separation. Such a procedure, while beneficial to improving hydroformylation activity, is not without the obvious drawbacks attendant with any phase separation and washing operation.
Additional methods that have been suggested for reactivating the rhodium catalyst of a hydroformylation reaction include the following.
U.S. Pat. No. 3,555,098 relates to maintaining or improving the rhodium catalytic activity of a hydroformylation reaction by washing all or a portion of a liquid medium containing the catalyst with an aqueous solution, e.g. an aqueous alkaline solution, to remove by-product acid, e.g. carboxylic acid, formed during hydroformylation by oxidation of the aldehyde which may have been due to oxygen contamination of the reactant gas stream.
Japanese Patent Application Publication No. 23,212/76 relates to maintaining or improving the rhodium catalytic activity of a hydroformylation reaction by removing the aldehyde from the distilled reaction product mixture containing the catalyst and then treating all or a portion of the liquid catalyst medium with oxygen during the recycling procedure of the catalyst back to the hydroformylation reaction.
U.S. Pat. No. 4,196,096 relates to a method for regenerating rhodium hydroformylation catalysts which comprises the steps of removing all or a portion of the inactive catalyst from the hydroformylation reaction, adjusting the aldehyde content so as to have at least one mole of aldehyde per mole of rhodium and ligand (e.g. triphenylphosphine) present and treating the aldehyde containing catalyst with oxygen or an oxygen containing gas at a temperature less than the boiling point of the aldehyde, removing any solid material formed during oxidation and adjusting the ligand to rhodium ratio as required for use in the hydroformylation reaction.
U.S. Pat. No. 4,221,743 relates to a hydroformylation process wherein the rate of productivity of the process can be maintained at a desired rate by feeding a sufficient amount of oxygen during the hydroformylation reaction to the homogeneous liquid phase composition of the reaction so as to maintain or increase the activity of the rhodium catalyst.
Note that U.S. Pat. Nos. 3,555,098 and 4,196,096 and said Japanese reference all teach that their reactivation procedure is carried out in a different vessel than the hydroformylation reactor and that none of the references discuss the detrimental effect of alkyl substituted phosphine in the hydroformylation reaction medium. Moreover, while the invention of above-mentioned U.S. Pat. No. 4,221,743 is carried out in the hydroformylation reactor vessel, said invention relates to a procedure conducted during the hydroformylation reaction and under hydroformylation conditions and also does not discuss the detrimental effect of alkyl substituted phosphine in the hydroformylation medium.